Peak images

June 17, 2017
 by Paul McGowan

Creatives climb aspirational mountain peaks by building mental images: authors through words, composers through music, designers through styling, engineers through schematics.

The peak I aspired to climb as far back as the early 90s was solving the age old problem of volume controls. Every scheme to date was a compromise: the sliding dissimilar materials of pots, multiple contacts of stepped attenuators, irregularities of light dependent resistors, loss of sonics with electronic pots. None were perfect. All were flawed.

At that point in time, I had narrowed my design thoughts to a scheme with fewer compromises. Using nothing more than a single high-quality resistor for the sound to pass through, it would be possible to build a volume control that eliminated the contacts, distortion, moving parts, and sonic loss of prior art. After all, I reasoned, music passes through a number of resistors on its journey to the power amplifier. Why not one more?

The problem with resistors and sound quality concerns resistance levels. The greater the series resistance the signal passes through the worse music sounds. I won’t get into the particulars that any engineer reading this post would pick up upon—like the load the resistor is working into—but take my word for it. Passing music through a 100kΩ series resistor sounds much worse than through a 100Ω part. Sound quality losses are immediately apparent.

In order to make a volume control with a single series element, you need to keep that element’s resistance relatively high so the corresponding shunt elements that funnel unwanted volume away can be effective. That resistance wound up requiring 30kΩ in order to give the product a reasonable attenuation range using electronic switches for the shunt elements. 30k is a very high series resistance and we’d need something special to make that work.

The experiments to find the perfect part began as Arnie Nudell and I auditioned numerous brands and types of resistors, finally settling on one. It was a handcrafted Vishay that, at the time, cost us $30 each (when even the best were about a dime) and we would need two.

The single element scheme and the Vishay worked. The volume control sounded far better than any pot we had heard, including the much talked about Penny and Giles. The bad news was it still had a sound to it. Even without any shunt elements, the single 30kΩ $30 Vishay placed its sonic thumbprint on the music. But, it was the best we had at the time, and better than any other technology available to us. We used that volume control in a product we called the Stealth Amplifier, a massive 200 Watt per channel Class A integrated Genesis produced. But I wasn’t satisfied.

The hunt continued, the peak yet climbed. What could be simpler and cleaner sounding for a volume control than just a single resistor?

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19 comments on “Peak images”

  1. Very interesting post tonight.. I feel like minimalist or passive preamps have made a comeback lately because it colors the sound less to have less stuff in the chain

    1. Indeed it was until a few months ago, the offer of passive preamps was high on eB, these days however has declined remarkably.

      Is it because the audiophiles prefer the active pre-amplifiers because of the intrinsic equalization they all produce?

      Do they prefer the euphonious colorations that the active pre-amp introduces?

      I know of more than one designer who departs from the manuals to design preamplifiers that sound good to the ears out of any other consideration. His favorite phrase was: “In audio nothing is written in stone” …

      We all know that the fully neutral active pre-amp has not yet been built, despite electronic volume controls, and all other advances.

    2. Passive preamps have other problems that make them unsuitable. Even the finest volume control needs an active buffer so as not to lose slam, bass and punch. Passive controls are clean but wimpy.

      1. @PM
        Moderator

        Why then did you make the PSA 6.0 which has a “wimpy” passive pre-amp along with the active pre-amp in a single chassis?

        After what you said today regarding passive pre-amps, it’s easy to imagine that it was just for market considerations. (Should it be?)

        1. If one were a cynic then I suppose that is true. If you’re actually interested in the answer, it was for purity of sound. The passive controls in our preamps were cleaner than those with the line stage, but had less impact and “wimpier” sound. Which is why we offered people a choice between the two.

          None were ever perfect and all had their good and bad points.

  2. IF passive preamps color the sound less, then why doesn’t any facturer build (only) passive preamps ?
    Probably because they do not color less. Or they have other flaws.
    And they still need a volume control (attenuator).
    I’ve had a few ones in the past (long time ago). And they colored the sound. I don’t know what was “wrong” in the design.

    1. There are of course highly renowned manufacturers of high end audio who offer alternative transformer (!) based volume control (TVC) designs as used in passive preamp from MF Audio or Bespoke Audio Company. See http://ypsilonelectronics.com/pst-100/ or Vinnie Rossi offering a TVC option for his LEO amp. I believed that the digital volume control in the DS-DAC would represent state-of-the-art volume control design until Paul McGowan himself revealed his preference for the classic volume control design used in the actual PS-Audio preamp. Funny. And don’t forget: there is no power supply based component in the audio chain that does distort (color) the source signal.

  3. That being said about resistance. Transformer probably the best
    Then again my preamp has only 1 stage, all other preamp have 2-3 stages.
    My preamp is completely transformer coupled it will pick up everything on the recording.
    I have 5 top notch transformers Heyboyer low power ,Lundahl Amphorous for audio section,
    And for power, plus 3 Lundahl filters or chokes,plus 80k in capacitance all 4pole capacitors
    Plus10 Mundorf Silver oil capacitors for bypass caps to further filter any high frequency noise.
    Neotech -0 crystal Copper wire throughout ,Khozmo shunt volume attenuator
    Using Takman resistors and 2 Vishay .5% on the out put relay control remote.
    And Russian 4P1L Vacuum tubes probablythe most Linear vacuum for a presmp and Very quiet .if made by a commercially made company an easy $15k and 50lbs in American Walnut
    This is what I consider best sound I have heard ,this tube being so linear ,but still Very natural
    Is slightly more forgiving in a bad recording. Great cables The new Verastarr Nemesis USB
    Review coming out in 3 weeks vs AQ Diamond and Wireworld PLATINUM. Verastarr my new Reference USB cable .

  4. While some makers claim perfection ps audio is one of the few that admits it’s all a trade off I tip my hat for there continued honesty
    Some designs do have more losses than others especially digital
    I have owned devices that the volume control did have negative effects on the sound as such I kept them turned up and used a passive active preamp. In my Msb dac I have an two sets of analog inputs. SE and bal same on output and there is settings for the used output method.
    Up to 0 DB is passive then beyond this point it’s active. The vol control is a stepped design in analog and can be set to 1/2 or 1 DB per click
    Sound quality seems to not be effected by active or passive stage
    Msb recommends like paul
    Did at one time to drive the amps or in my case outboard cross over directly. I use this method but others who own it do claim better can be had with a preamp. I think all of our devices are shades of color and this is more about taste then better or not. I also use the Msb to convert from SE to bal to use my lampi it’s needed as my lampi is only SE and my output cables are 25 feet so bal is a must something that is clearly heard if I try SE cables beyond 6 feet. The vol control and the inputs are all options. When I use my lampi I kept its vol at max and use the Msb for attenuation. Although using it alone and keeping the Msb at 0db seems fine too. I empithise with paul on choices for design and there costs. I do get how some devices may sound better in some situations. Great topic paul

  5. I had the Placette passive volume controller in my system for years. It used Vishay resistors and provided ultra clear sonics. The problem was that it would run out of gain on certain discs. I had forgotten the dynamics I lost during this time until I replaced it with an active preamp. Whatever its failings, the preamp is the heart of the system, and there is no replacing it.

  6. Paul asks: The hunt continued, the peak yet climbed. What could be simpler and cleaner sounding for a volume control than just a single resistor?

    Yodlers?

  7. Sorry…. Nothing is neutral but sitting in the actual live performance. And, neutral may not be always good. I have heard very boring live performances.

    Build something that makes them feel happy inside and they will come. Sound Field of Dreams?

  8. I hate to admit it, but what Paul says about resistor volume controls at lower volumes may be what I have experienced. With my old preamp, a highly upgraded Nobis Proteus, with the Dact volume control, I always liked that it sounded good at low volumes. Good thing as I was living in a duplex with a neighbor above me. Lately I have been playing my system louder, partly because with the Lindemann it has never sounded better, but it takes more volume for it to come alive. Partly a lower output than the Benchmark Dac2, that I ran with the volume wide open, rather than using the option that held the volume to one setting. I don’t think it bypassed the volume control so I preferred it wide open.
    I now live in a house so I can play at any volume I choose, well now that I am single again I can. I don’t miss the can’t you turn that down, and that was with the old preamp with the Dact at it’s lowest setting. A very good volume controller, but it really needed more steps, at tighter increments.

    I never considered that the lack of dynamics at lower volumes was due to anything other than my ears getting older. And as to louder, sounding better, because of less noise and distortion. It is kind of an oh well situation. Right now I’m listening to Green Day on Tidal, a Master of “Ono Dos Tre’s” that sounds “F”ing great, even sitting in the corner with the balance way to the right. If my financial situation changes, I may have to audition the BHK preamp. I kind of thought I would stay in the Conrad Johnson family, but??? I tend to find a component that I like, and then become very loyal to it. Even though the Nobis was a $2000 preamp, with a bit of tube hiss that could be heard if you were within a foot of the speakers, I thought it would be the last thing I would replace, until I put the CT5 in. The quiet, the inner detail, I had a new love, still do;-)

  9. Paul, independent of the volume resistor example, I always wondered what importance the most reduced use of electronic parts generally has, speaking just about active designs.

    It’s hard to count and compare them especially in SMD solid state designs, but seeing some expensive and overly packed tube designs in comparison to i.e. an insanely expensive nearly empty Audio Note Kondo I’m helpless to judge what role many or lesser parts play.

    Many parts often allow more sophisticated designs and therefore are better and more expensive than components with lesser parts?

    Or the opposite: it’s much more difficult to make great reduced designs which benefit from lessser parts and terefore they are better than good designs with many parts?

    Or doesn’t the number of electronic parts play a role as long they are not directly in the signal path, which mostly is designed part reduced?

    1. Vandersteens amps, the one’s that are designed only to be used with model 7, has only 5 components in the signal path, but lots of other stuff. Probably the power supply and for the liquid cooling.
      I sometimes look at a component with hundreds of parts, and wonder if they just keep adding to correct what something further back is doing wrong.

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